1. Field of the Invention
The invention relates to a laser welding device for metal parts, in particular for flat contact plugs according to the preamble statement of claim 1, a process and a device for the manufacture of flat contact strip according to the preamble statement of claim 7 respectively of claim 8, as well as flat contact plugs according to the preamble statement of claim 9.
2. Description of the Prior Development
Such laser welding devices for metal parts are inter al, used for the automated manufacture of flat contact plugs formed from steel strip in order to connect links which are bent or folded together and which are subsequently to form the shoulders of such flat contact plugs in the area of the joint gap. Such a flat contact plug 1 which is shown in horizontal projection in FIG. 3 has a plug shoulder 2 which stretches in the direction of plug insertion and which consists of an underside base part and two side links 4, 5 bent together on the said base part. As can be seen from FIG. 2a which shows a section of the plug shoulder during the process of bending, both the links 4,5 which are formed onto the base part 3 are bent so far that their longitudinal edges 7,8 push against one another or form a joint gap which runs along the longitudinal axis 9. This condition is shown in section in FIG. 2b. The process of folding or the bending deformation of the links 4,5 did not hitherto yield an adequate permanence of shape, so that after numerous insertions and withdrawals of the flat contact plug, a separation of the folded links occurred.
In order to avoid these problems, the bent links 4,5 are at present being spot-welded with the help of a vertically directed laser beam, where the welding point 10 is placed centrally between the longitudinal edges 7,8 of the links 4,5 on the free end of the plug shoulder 2 (cf FIG. 3). For this welding procedure, the laser unit or a deflection reflector is arranged vertically over the plug shoulder to be welded. In order to avoid collision with the folding tool which also works vertically, certain minimum distances must be observed which give rise to problems of position and space. In addition, it is a drawback that the vertically-directed laser beam produces circular welding points 10 which do not ensure a firm connection of the link edges 3,4. Correspondingly, separations of the links can occur in flat contact plugs which have been manufactured in this way. The vertical arrangement of the laser unit or of the optical deflection reflectors also brings it about that the rising metal vapours formed in the process of welding deposit as a coating on the surfaces of the laser components and thereby adversely affect the penetration of light. This leads to a fall in the output of the laser and to the formation of correspondingly weaker welded joints, since in the course of time, the laser output is absorbed by the laser lens and ceases to be available for welding.
U.S. Pat. No. 5,053,601 discloses a laser beam device which is integrated into a stamping device for metal parts. The laser unit is located at the side above the stamping device and the laser beam impinges sideways at an acute angle on the piece concerned. This known installation is however unsuitable for the manufacture of flat contact plugs and in particular for that of flat plug strips, since it possesses neither a means of folding or bending of side links nor a means of rhythmical movement.
It is the purpose of the invention to create a laser welding device which produces improved welded joints whilst needing less space and hardly at all soiling the lenses. This purpose is accomplished through the characteristics of the independent claims 1 and 8.
The invention has the further purpose of improving the process of manufacture of flat contact plugs in such a way that strong permanent welded joints are produced and after prolonged operating times and a high rate of insertions and withdrawals, the undesirable separation of the links is effectively prevented.
This purpose is accomplished by the use of the process steps contained in claim 7.
The laser welding device according to the invention can advantageously be integrated in compact stamping and folding installations such as those used in the mass production of flat contact plugs. Due to the angled direction of the laser beam, it is possible to position the laser unit sideways outside the mostly vertically moving stamping and folding tools and furthermore, metal vapours and other particulate contaminants which develop during the process of welding are prevented from depositing on the laser optical system. This ensures a constant laser output even over a prolonged period of use. Moreover, the laser unit can be optimally positioned in relation to the other manufacturing units which brings about an overall reduction in the size of the installation.
FIGS. 4a and 4b show a plug shoulder in IIxe2x80x94II line section in FIG. 3; FIG. 4a shows a welding point 10a made according to the invention and FIG. 4b shows a welding point 10b made conventionally using a vertically directed laser beam. According to the state of the art, the melted welding point 11b of the welding point 10b only stretches as far as the link edges and only to the surface area of the base part 3, whereby a small amount of molten metal is forced into the air gap between the base part 3 and both the links 4,5. On the other hand, the welding point 10a shown in FIG. 4a and made using the laser welding device according to the invention, is substantially more stable since its substantially greater welding range 11a penetrates more deeply into the link edges and the base part 3 penetrates as far as the underside. The increased amount of molten material leads to a correspondingly increased strength of the welded joint. Moreover, the welding points are, in the case of assembly line or mass production, of permanently high quality since the optical components of the laser unit are not soiled by deposits of metal or other contaminants.
Advantageous embodiments and developments of the invention are set out in dependant Claims.
Preferred embodiment examples of the invention are explained individually in the schematic drawings: